The genetic testing startup founded by the wife of Google billionaire Sergey Brin has received a further $2.6m investment from the internet giant.

In documents filed with the US Securities and Exchange Commission, Google said it had increased its shareholding in 23andMe, the DNA decoding company started by Anne Wojcicki, who married Brin in 2007. The latest investment comes on top of $3.9m that Google put into the company two years ago.

The company has been hotly-tipped as one of a new wave of genetic testing outfits, which offer paying customers the chance to decode parts of their genome - with the aim of revealing certain genetic anomalies or predispositions.

However, Google's continuing investments in 23andMe are likely to raise questions of a conflict of interest among the company's shareholders, particularly since the Californian technology giant is using its money to back a personal project that benefits the family of Brin - who has a personal fortune estimated at $12bn.

Brin has already pumped significant sums of his own into 23andMe, including $10m used to finance some of the company's debt - but part of Google's investments have been used to repay loans he made to his wife's company.

Although the Brin has remained relatively quiet on the subject of 23andMe, last year he broke his silence to say that a 23andMe test had revealed he is genetically predisposed to Parkinson's Disease - a condition that has drastically affected the life of his mother since she was diagnosed 10 years ago.

Brin, who is 35, said the test results had convinced him to pump money into further research into Parkinson's.